A prosthesis with flexibility and optimal proximal fit was constructed in titanium alloy. The aim was to create the same elasticity as in the femoral shaft. Distally it was cylindrical with slots in the stem and a spacer made of polymer was placed in the slots. The proximal part of the prosthesis was wedge-shaped in both planes and a collar with a conical contact surface to bone was used. Pure titanium was plasma sprayed on the upper part as well as underneath the collar allowing bony ingrowth. A test jig was constructed and 10 million cycles with 4000 N loading was planned. The prosthesis broke after 600 000 cycles and it was a typical fatigue failure. A commercially available flexible prosthesis was tested as a reference and broke after 29 000 cycles. It is concluded that construction of a flexible hip prosthesis using metal with reasonable security against fatigue failure breakage is difficult, and we are somewhat doubtful if it is possible.
[1]
J. Gillquist,et al.
A prospective comparison of Butel and PCA hip arthroplasty.
,
1993,
The Journal of bone and joint surgery. British volume.
[2]
J. G. Andrews,et al.
A biomechanical investigation of the human hip.
,
1978,
Journal of biomechanics.
[3]
J. Gillquist,et al.
Calcar unloading after hip replacement. A cadaver study of femoral stem designs.
,
1987,
Acta orthopaedica Scandinavica.
[4]
J. Butel,et al.
The isoelastic hip prosthesis followed for 5 years.
,
1988,
Acta Orthopaedica Scandinavica.
[5]
D T Davy,et al.
Telemetric force measurements across the hip after total arthroplasty.
,
1988,
The Journal of bone and joint surgery. American volume.
[6]
N. Rydell.
Forces acting on the femoral head-prosthesis. A study on strain gauge supplied prostheses in living persons.
,
1966,
Acta orthopaedica Scandinavica.